JPH11177521A - Transmitter-receiver for ofdm broadcast - Google Patents

Abstract

PROBLEM TO BE SOLVED: To multiplex the non-real time data into the phase modulated signals via the modulation of amplitude by making a transmitting part receive only the phase modulating signals to perform the compatible multiplexing even when a receiving part cannot separate the received signals into the phase and amplitude modulating signals. SOLUTION: A receiver 30 receives the transmitted signals via an antenna 11, amplifies the received signals via a high frequency amplifier 12, applies the down conversion to the received signals via a mixing part 13 and a local oscillator 14 and inputs the converted signals to a fast Fourier transform part 16 via a band pass filter 15. The part 16 applies the Fourier processing to a specific expression to output A1 Q1 , A2 I2 ...An In , An Qn to every subcarrier. A phase calculation part 17 performs a prescribed operation to demodulate a phase. In this case, the amplitudes of (Ik , Qk ) is just changed into Ak for the phases of (Ak Ik , Ak Qk ) and equal to the phases of (Ik , Qk ) to never change despite a modulated amplitude.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) broadcast wave transmitting / receiving apparatus, and more particularly to an OFDM broadcasting transmitting / receiving apparatus capable of multiplexing data other than a broadcast signal.

[0002]

2. Description of the Related Art Broadcasting using OFDM has been put to practical use in DAB (digital audio broadcasting) and the like. That is, OFDM is composed of a number of orthogonal subcarriers, and each subcarrier is modulated by QPSK (quadrature phase modulation) or the like. A fixed number of modulated subcarriers form a symbol, and a large number of symbols form a frame. The subcarriers in symbol units are modulated by the inverse Fourier (IFFT) processing, and the subcarriers are demodulated by the Fourier processing. Note that OFDM has mode I as an operation mode.
~ III.

[0003] In FM multiplex broadcasting, real-time audio broadcasting is not required for content that is broadcasted in real time (non-real-time). For example, image information such as text and graphics, audio signals, traffic information, and the like are not required. Data is multiplexed in the form of a digital signal. For this reason, a wide variety of services are provided using existing broadcasting devices and receiving devices.

[0004]

The above-described multiplexing function in FM multiplex broadcasting is effective if it is also provided in a transceiver for OFDM broadcasting. Therefore, the present invention provides an OFDM multiplex broadcast transmission / reception apparatus capable of multiplexing another content composed of data that does not require real-time with the same broadcast frequency with respect to already-broadcasted real-time audio broadcast content. The purpose is to: Even if this multiplexing is realized, it is important that real-time reception can be continued even for a receiver that can only perform real-time reception.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to an OFDM broadcast transmitting / receiving apparatus for transmitting a broadcast wave obtained by phase-modulating a number of orthogonal subcarriers and receiving the broadcast wave. A transmitting unit that forms a broadcast wave in which data is multiplexed by amplitude modulation with respect to a phase modulated signal that has been modulated with data, and receives a broadcast wave transmitted from the transmitting unit, and outputs a phase modulation signal and an amplitude modulation signal. A receiving unit that performs a process of separating and extracting the received signal, the transmitting unit receives the phase modulated signal only, even if the receiving unit cannot separate the received signal into the phase modulated signal and the amplitude modulated signal. Provided is an OFDM broadcast transmitting / receiving apparatus that performs multiplexing with compatibility so as to enable the multiplexing. By this means, it has become possible to multiplex data into OFDM broadcasts. Note that the phase modulation signal may be formed in real time, and the amplitude modulation signal may be formed in non-real time.

[0006] The transmitting unit uses a broadcast wave based on a phase-modulated signal as basic information, multiplexed information based on amplitude modulation as supplementary information for the basic information, and further uses a broadcast wave based on a phase-modulated signal as basic information. And multiplexed information based on the amplitude modulation signal are assumed to be independent information. By this means, various new services can be added. The transmission unit accumulates data used for amplitude modulation as the independent information, and repeatedly multiplexes data having the same content into a phase modulation signal. By this means, the reception rate can be improved.

[0007] The transmitting section performs differential encoding of the amplitude modulation with time, and the receiving section demodulates the differential encoding of the transmitting section. By this means, it is resistant to slow fading. The transmitting unit performs differential encoding on the amplitude modulation in the direction of the frequency of the subcarrier in the symbol, and the receiving unit demodulates the differential encoding of the transmitting unit. By this means,
Strong against steep fading.

[0008] The transmitting section performs modulation processing by performing an inverse Fourier transform process on the signal obtained by multiplexing the amplitude signal with the phase modulated signal, and the receiving section performs a Fourier transform on a received signal from the transmitting section. Demodulation processing for separating the phase modulation signal and the amplitude modulation signal. By this means, the modulation and demodulation of the multiplexing by the amplitude modulation with respect to the phase modulation signal can be easily performed.

The receiving unit sets a threshold value used when converting the amplitude obtained by demodulating the differential encoding of the transmitting unit into 1-bit data, as an average value of temporally or frequency-adjacent amplitudes. And By this means, the threshold follows the fluctuation of the fading, so that the threshold is further improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an OFDM according to the present invention.
QP to each subcarrier in multiplex broadcast transmitting / receiving device
FIG. 9 is a diagram illustrating an example of a broadcast side that multiplexes data by amplitude modulation with respect to SK modulation. The broadcast apparatus 10, as shown in the figure, the data _{I 1, Q 1, I 2} , Q 2 ... I n, the conventional content data storage unit 1 for outputting a Q _n of audio broadcasting for audio broadcast in real time Provided. An inverse fast Fourier transform unit 2 connected to the conventional content data storage unit 1 forms a baseband signal waveform of one symbol by the following equation based on audio broadcast data.

[0011] Here, ω _K is the k-th subcarrier angular frequency in the baseband, and in the case of mode I, n = 1536
It is.

[0012] Multiple content data storage unit 3 outputs the enhancement data A _1, A ₂ ... A _n for reinforcing the data from a conventional contents data storage unit section 1. For example, when voice information of traffic information is being transmitted from the conventional content data storage unit 1, display data for displaying traffic congestion information on a road map is output. When the voice information indicates shopping, display data for displaying a map around shopping is output.

The multiplexed content data storage unit 3 may output data independently of the data from the conventional content data storage unit 1. For example, there is display data of a weather forecast, a result of sports, and a summary of news, and may be used for calling a pager. Output I ₁ from the output A _1, A ₂ ... A _n the conventional content data storage unit 1 in the 2n multipliers 4 of multiplexed contents data storage unit _{3, Q 1, I 2,} Q 2 ... I n, Multiplied by Q _n , A
_{1 I 1, A 1 Q 1} , A 2 I 2, A 2 Q 2 ... A n I n, A
_n Q _n , and the result is input to the inverse fast Fourier transform unit 2. The above equation (1) is as follows.

[0014] The result processed by the inverse fast Fourier transform unit 2 is up-converted by the mixing unit 5 and the local oscillator 6, and transmitted to the receiving device via the amplifier 7, the band-pass filter 8, and the antenna 9.

FIG. 2 shows data I _K and Q _K used for the QPSK modulation shown in FIG. 1 and their amplitude-modulated data A _K.
I _K, is a diagram for explaining the A _K Q _K. As shown in the figure, for the rectangular coordinates, (I _K , Q _K ) = (1, 1),
As in (-1, 1), (-1, -1), and (1, -1), the conventional content data storage unit 1 outputs 2-bit data for each subcarrier. (1,
Each phase of 1) and (-1, -1) is φ _K = tan ^-1 (I _K / Q _K ) = ± 45 °, and each phase of (−1,1) and (1, −1) The phase is φ _K = tan ⁻¹ (I _K / Q _K ) = ± 135 °. Multi-content data storage 3
Output of the conventional content data storage unit 1 is (A _K
I _K , A _K Q _K ) = (A, A), (−A, A), (−
A, -A) and (A, -A).

[0016] FIG. 3 is a diagram illustrating an example of forming an amplitude A _K of the multi-contents data storage unit 3 of FIG. This, as shown in FIG. (A), multiplexed content data D ₁ of one or 0, D ₂ ... multiplier for each of the D _n 31-1
Is multiplied by A, and 1 is added to each of the multiplied results by the adder 31-2. As shown in FIG. 3B, the multiplexed content data D ₁ ,
Amplitude A ₁ with respect to _{D 2 ... D n, A 2} ... A n is formed. In this way, each of A _K takes a value of A (> 1) or 1, and has 1-bit amplitude information.

FIG. 4 is a diagram showing an example of a subcarrier spectrum of one symbol multiplexed by amplitude modulation. First, in the example of the mode I of OFDM, one frame is composed of a header, a symbol and 76 symbols, and one symbol is composed of 1536 subcarriers. The length of one frame is about 961 ms, and the length of one symbol is 1 ms. FIG. 3A shows the amplitude of the subcarrier of one symbol, FIG. 3B shows the amplitude of the amplitude modulation signal corresponding to the subcarrier, and FIG. 3C shows the amplitude of the subcarrier. The amplitude of the signal A ′ obtained by modulating the amplitude-modulated signal on the phase-modulated signal is shown.

FIG. 5 is a diagram for explaining an example of a receiving side for extracting multiplexed data by amplitude demodulation from a transmission signal from the broadcasting side in FIG. As shown in FIG.
The transmission signal is received by the antenna 11 and the high-frequency amplifier 12
, A down-converted by the mixer 13 and the local oscillator 14, and input to the fast Fourier transformer 16 via the band-pass filter 15.

The fast Fourier transform unit 16 performs a Fourier process on the equation (2), and calculates A ₁ I ₁ ,
A ₁ Q ₁ , A ₂ I ₂ ,... A _n I _n , A _n Q _n are output. Phase calculating unit ^{_{17, φ K = tan -1 {(}} A K I K) / (A K Q K)} = tan -1 performed (I _K / Q _K) becomes operational, demodulates the phase. As described above, it is amplitude _{modulated, (A K I K, A} K Q K) of the _{phase, (A K I K, A} K Q K) relates the above-described (I _K,
Since the amplitude of Q _K ) has just changed to A _K ,
It is the same as the phase of (I _K , Q _K ) and does not change. That is, even if such amplitude modulation is performed, similar reception is possible with a conventional receiving apparatus, that is, compatibility is ensured.

The decoder 18 has a φ_K== 45 ° and 00
And φ_K= −45 ° is 10 and φ _K= + 135 ° to 0
1 and φ_K= -135 ° is 11 and each subcarrier
2 bits of each phase are converted to data for conventional contents
You. The amplitude calculator 18 calculates A_K'= ｛(A_KI_K)^Two+ (A_KQ_K)^Two｝^1/2 = CA_K(∵I_K ^Two+ Q_K ^Two= C^Two(Constant)), and the decoder 20 outputs the amplitude A_KMany
Convert to heavy content data. In this case, A_K= A
Then A_K'= CA_K= 1 then
A_K'= C.

FIG. 6 is a diagram for explaining an example of converting the amplitude _AK into 1-bit data, and FIG. 7 is a diagram for explaining the threshold value Vr. As shown in FIG. 6A, the amplitude A _K ′ is set to a constant threshold value Vr (C <Vr <C · A:
As shown in FIG. 6B, the amplitude A _K ′ is changed to 1-bit data D _K in comparison with FIG. Therefore, according to the above-described embodiment, data can be multiplexed by modulating also in the amplitude direction while maintaining the phase of the subcarrier.

If the data for multiplexed content that does not require real-time is data that is used independently of real-time audio broadcasting, the broadcasting side stores the data in a memory (not shown) and stores the stored data. It may be used to rebroadcast the same information many times. Thereby, the reception rate of the multiplexed content data is improved. Next, a countermeasure against fading for the present invention will be described. As shown in FIG. 5, when converting the amplitude A _K ′ into 1-bit data, the threshold value Vr is used, but the amplitude A _K ′ varies under the influence of fading. That is, despite the amplitude A _K ′ = C · A, the fading causes the amplitude to drop and the amplitude A _K ′ falls below the threshold value Vr, and conversely, regardless of the amplitude A _K ′ = C, the fading occurs. , The amplitude A _K ′ may exceed the threshold value Vr. The solution will be specifically described below.

FIG. 8 is a diagram for explaining an example in which the amplitude is differentially modulated in the multiplexed content data storage section 2 on the broadcast side. As shown in the figure, to each of the input side of the multiplier 31-1 of FIG. 3, the adder inputs the _{D 1, D 2 ... D n} 31-3
And an absolute value converting section 31-4 for converting the output of the adder 31-3 to an absolute value and outputting the result to the multiplier 31-1, and delaying the output of the absolute value converting section 31-4 by one symbol period. A memory 31-5 is provided for inverting the positive / negative sign and inputting the inverted signal to the other of the adder 31-3. In this way, the differential encoding is performed based on the data to be modulated on the subcarrier of the previous symbol and the subcarrier of the current symbol.

FIG. 9 is a diagram for explaining an example in which the decoder 20 on the receiving side performs differential demodulation of the amplitude with respect to the differential modulation shown in FIG. As shown in the figure, the comparator 20-
Each one of the input side, an amplitude _{A 1 ', A 2' ...} ' adder 20-2 for inputting the amplitude A _1' A _n, A ₂ and enter the '... A _n' 1 symbol period delayed A memory 20-3 for inverting the positive and negative signs and inputting the inverted signal to the other end of the adder 20-2;
An absolute value conversion unit 20-4 for converting the output of the adder 20-2 to an absolute value and inputting the result to the comparison unit 20-1 is provided. Thus, differential demodulation is performed on the differential modulation shown in FIG.

FIG. 10 is a time chart for explaining the differential operation of the configuration shown in FIGS. As shown in the drawings (a) and (b), on the transmitting side, differential modulation is performed on the multiplexed content data D _k of the subcarrier k in the symbol i (i = 1 to 76). , (D),
Differential demodulation is performed. FIG. 11 is a diagram for explaining the effect on fading between symbols. As shown in the figure, when the fading is gentle, the fluctuation of the amplitude of the subcarrier between the distant symbols becomes large, but the fluctuation of the amplitude of the subcarrier between the adjacent symbols becomes small. Therefore, the influence of such gradual fading during transmission is very small due to the differential modulation and demodulation of the amplitude.

FIG. 12 is a view for explaining another example in which the amplitude is differentially modulated in the multiplexed content data storage section 2 on the broadcast side. As shown in the figure, the _{D 1, D 2, D 3} ... adder 31-5 for inputting D _n-1, D _n on each of the input side of the multiplier 31-1 of FIG. 3, the result of the addition An absolute value part 31-7 for converting the result into an absolute value and outputting the result to a multiplier 31-3 and an adjacent adder 31-5 is provided. In this way, differential encoding of data is performed on adjacent sub-carriers in one symbol.

FIG. 13 shows the receiving side for the differential modulation shown in FIG.
Of performing differential demodulation of amplitude in decoder 20 of FIG.
FIG. As shown in the figure, the comparator 20-1 of FIG.
At each input side of₁’, A_Two’, Amplitude A_Two’,
A_Three’,... Amplitude A_n-1’, A _n’And enter the difference
Adder 20-5 for calculating the minute and converting the addition result to an absolute value
And an absolute value conversion unit 20-6 for outputting the result to the multiplier 20-1.
Be killed. In this way, the differential modulation of FIG.
A minute demodulation is performed.

FIG. 14 is a time chart for explaining the differential operation of the configuration shown in FIGS. This figure (a),
As (b), the differential modulation is performed on the multiplexed content data D _k of subcarriers k at subcarrier k in one symbol (k = 1-1,536) is the transmitting side, the view (c), ( As shown in d), differential demodulation is performed.

FIG. 15 is a diagram for explaining the effect on fading in a symbol. As shown in the figure, when the fading is steep, the fluctuation of the amplitude is large between distant subcarriers, but the fluctuation of the amplitude is small between adjacent subcarriers. Therefore, the influence of such steep fading during transmission is very small due to the amplitude modulation / demodulation.

The output of the absolute value conversion 20-4 in FIG. 9 and the output of the absolute value conversion 20-6 in FIG. 13 are A or 1, and A or 1 is random. The threshold value Vr of the comparator 20-1 in FIGS. 9 and 13 may be obtained. In this averaging, the outputs of several to several tens of absolute values 20-4 or 20-6 adjacent to each other are averaged, and
This may be obtained as the threshold value Vr. As described above, the threshold value Vr can follow the fluctuation of the fading, and is hardly affected by the fading in addition to the above-described differential coding.

The QPSK has been described above.
The present invention is applicable to shift QPSK and other phase modulation.

[0032]

As described above, according to the present invention, the OF
Non-real-time data can be multiplexed into a phase-modulated signal by amplitude modulation in DM broadcasting, and multiplexing that is strong against fading can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a broadcast side that multiplexes data by amplitude modulation with respect to QPSK modulation for each subcarrier in an OFDM multiplex broadcast transmitting / receiving apparatus according to the present invention.

FIG. 2 shows data I _K , used for the QPSK modulation of FIG.
Q _K and these amplitude-modulated data A _K I _K and A _K
It is a diagram illustrating a Q _K.

FIG. 3 is a diagram illustrating an example of forming an amplitude A _K of the multiplexed content data storage unit 3 of FIG. 1;

FIG. 4 is a diagram illustrating an example of a subcarrier spectrum of one symbol multiplexed by amplitude modulation.

FIG. 5 is a diagram illustrating an example of a receiving side that extracts multiplexed data by amplitude demodulation from a transmission signal from a broadcasting side in FIG. 1;

FIG. 6 is a diagram illustrating an example of converting amplitude A _K into 1-bit data.

FIG. 7 is a diagram illustrating a threshold value Vr.

FIG. 8 is a diagram illustrating an example in which amplitude is differentially modulated in the multiplexed content data storage unit 2 on the broadcast side.

9 shows a decoder 20 on the receiving side for the differential modulation of FIG.
FIG. 4 is a diagram for explaining an example of performing differential demodulation of amplitude in FIG.

FIG. 10 is a time chart for explaining the differential operation of the configuration of FIGS. 8 and 9;

FIG. 11 is a diagram illustrating an effect on fading across symbols.

FIG. 12 is a diagram illustrating another example in which the amplitude is differentially modulated in the multiplexed content data storage unit 2 on the broadcast side.

13 is a diagram illustrating an example in which amplitude demodulation is performed in the decoder 20 on the receiving side with respect to the differential modulation in FIG.

FIG. 14 is a time chart for explaining the differential operation of the configuration shown in FIGS. 12 and 13;

FIG. 15 is a diagram illustrating an effect on fading in a symbol.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Conventional content data storage unit 2 ... Multiple content data storage unit 3 ... Inverse fast Fourier transform unit 16 ... Fast Fourier transform unit 17 ... Phase operation unit 18 ... Amplitude operation unit 19, 20 ... Decoder

Claims (9)

[Claims] An OFDM broadcast transmitting / receiving apparatus for transmitting a broadcast wave obtained by phase-modulating a number of orthogonal subcarriers and receiving the received signal is amplitude-modulated with respect to a phase modulated signal modulated with broadcast wave data. And a receiving unit that receives the broadcast wave transmitted from the transmitting unit, and separates and extracts the phase-modulated signal and the amplitude-modulated signal from the transmitting unit. Performs compatible multiplexing so that only the phase-modulated signal can be received without the receiver having a function of separating the received signal into the phase-modulated signal and the amplitude-modulated signal. An OFDM broadcast transmitting / receiving apparatus, characterized in that: 2. The transmission unit according to claim 1, wherein the transmission unit uses a broadcast wave based on a phase modulation signal as basic information, and uses multiplexed information based on amplitude modulation as supplementary information of the basic information. OFDM broadcast transmitting and receiving device. 3. The transmission unit according to claim 1, wherein the transmission unit sets the broadcast wave based on the phase modulation signal as basic information and the multiplexed information based on the amplitude modulation signal as independent information. An OFDM broadcast transmission / reception device. 4. The transmission unit according to claim 4, wherein the transmission unit accumulates data used for amplitude modulation as the independent information, repeats data having the same content, and multiplexes the data with a phase modulated signal. The transmission / reception apparatus of the OFDM broadcast according to the above. 5. The OFDM according to claim 1, wherein the transmitting unit performs differential encoding of the amplitude modulation with respect to time, and the receiving unit demodulates the differential encoding of the transmitting unit.
Broadcasting transceiver. 6. The transmitter according to claim 1, wherein the amplitude modulation is differentially encoded in the direction of the frequency of a subcarrier in a symbol, and the receiver demodulates the differential encoding of the transmitter. An OFDM broadcast transmitting / receiving apparatus according to claim 1. 7. The transmitting unit performs an inverse Fourier transform process on a signal obtained by multiplexing the amplitude modulated signal on the phase modulated signal, and performs a modulation process, and the receiving unit performs a Fourier transform on a received signal from the transmitting unit. The transmission / reception apparatus for OFDM broadcast according to claim 1, wherein demodulation processing for performing conversion to separate a phase modulation signal and an amplitude signal is performed. 8. The receiving unit sets a threshold used when converting the amplitude obtained by demodulating the differential encoding of the transmitting unit into 1-bit data, by using a threshold value of a temporally or frequency-adjacent amplitude. 2. The OF according to claim 1, wherein the OF is an average value.
Transmitter / receiver for DM broadcast. 9. The transmission / reception apparatus according to claim 1, wherein the phase modulation signal is formed in real time, and the amplitude modulation signal is formed in non-real time.